The present invention relates to a drive assembly for a motor vehicle comprising a forward engine supported in bearings on the vehicle body, a rearward drive unit supported by way of at least one elastic bearing, and a central support tube arranged in-between which is connected on the forward end with the engine in a movable manner and on the rearward end with the drive unit in a rigid manner, and in which a drive shaft extends which has a torque-transmitting joint in the area of its connection to the clutch shaft.
From German Patent Document DE-PS 34 17 227, a drive assembly for a motor vehicle is known which comprises a forward engine and a rearward transmission, and these units are connected by way of a center tube. Inside the tube, a drive shaft is arranged which establishes a driving connection between the engine and the transmission. In order to avoid the transmitting of low-frequency vibrations from the engine to the transmission, particularly when driving over bumps or the like, a torsionally rigid and thin-walled corrugated metal tube is used which, however, cannot be designed in a targeted manner with respect to the main excitation directions of the engine but represents an articulated connection.
It is an object of the invention to provide a drive assembly which ensures a targeted uncoupling of vibrations of the engine, particularly high-frequency vibrations caused by unbalanced forces of inertia and moments of inertia, with respect to the remaining drive assembly.
This and other objects are achieved by the present invention which provides a drive assembly for a motor vehicle comprising a forward engine supported in bearings on the vehicle body, a rearward drive unit supported by way of at least one elastic bearing, and a central support tube arranged in-between which is connected on the forward end with the engine in a movable manner and on the rearward end with the drive unit in a rigid manner, and in which a drive shaft extends which has a torque-transmitting joint in the area of its connection to the clutch shaft, wherein the engine is connected with the drive unit by way of a vibration uncoupling device which can be adapted as a function of main excitation directions of the engine in the circular direction in the vertical Z-direction and in the transverse Y-direction, and which comprises a connecting joint which holds the engine so that it can be angularly moved in main excitation directions, and the connecting joint and/or a bearing device is used for the torque support of the drive unit, the bearings of the engine and of the drive unit being arranged in vibration nodes of the natural vibrations of the assembly and a largest possible supporting base with the distance existing between the bearings of the drive unit in an elastic bearing on the central support tube, the bearing being arranged on the joint part of the central support tube.
The principal advantages achieved by means of the invention are that the disadvantages of the central support tube concept with respect to the excitation of vibrations are avoided, but at the same time, the advantages which are typical of the central support tube are maintained. These consist particularly of a low number of bearing points of the assembly in the vehicle and of a large supporting base for the wheel drive torques.
Pronounced bending and torsional resonances of the overall assembly which are preferably excited by the engine usually occur in the operating rotational speed range. In order to avoid these resonances, the assembly is divided into two vibration systems in such a manner that the engine is uncoupled by means of an uncoupling device, such as a connecting joint, from the remaining assembly, such as the transmission with the connected central support tube. This device or this joint must be coordinated in such a manner that the main excitation directions or planes of the engine in the vertical and transverse direction as well as during wobbling excitations are taken into account.
Thus, according to the construction of the engine and its main excitation directions, a joint may advantageously be inserted by means of which a torsionally rigid uncoupling is achieved that is free of bending moments, either in a Y-plane or in a Z-plane. Another embodiment contains a joint which causes a torsionally rigid uncoupling that is free of bending moments simultaneously in a Z-plane and a Y-plane. A construction of a joint, such as an elastic ring, is also possible by means of which an uncoupling is achieved which is torsionally soft and free of bending moments.
In the case of a torsionally soft uncoupling of the engine, a vehicle-body-side support by way of two bearings arranged on a console is required for the supporting of the engine driving torques in the area of the transmission.
The connecting joint should be arranged as close to the engine as possible in order to avoid large paths on the joint when the engine is moved. Also, an additional bearing should be arranged on the central support tube which has a base to the rear bearing of the transmission that is as large as possible.
According to the requirements, the connecting joint may be an O-seal, an elastomer preform or a flexible disk.
The articulated connecting of the central support tube by means of an O-seal made of an elastomer material takes place in such a manner that the ring is inserted in a connecting flange of a bell housing which centers in a flange-free manner the central support tube by way of the inside diameter.
According to another embodiment, the connecting joint may also be constructed as a spherical plain bearing comprising an outer ring and an inner ring which each have arched slide faces and permit a wobbling motion of the engine caused by free inertial forces to the central support tube with the connected transmission.
As a result, the bearing points of the transmission are largely kept free of bending vibrations. The spherical plain bearing is constructed in such a manner that it is radially without play but can transmit axial forces and is constructed to be extremely free of friction.
The arrangement of the spherical plain bearing is provided at the free end of the central support tube which faces the engine, the inner ring being held in a receiving device which is connected with the central support tube. This receiving device may consist either of a sleeve which can be fitted onto the tube or of a lengthened tube part.
At the end, the exterior tube is supported on the clutch housing and is held by a tensioning ring which is connected with a clutch housing. So that the bearing arrangements on the inner ring can be carried out in a simple manner, this inner ring has longitudinal slots which permit a sliding onto the arched slide face of the inner ring.
A rubber O-seal inserted in a groove on the outer ring of the bearing prevents by means of its prestressing a rattling play in the housing parts. Furthermore, it achieves that freedom from play is obtained in the bearing during its whole service life.
In the case of a crash at low speed, a transmission of forces from the engine by way of the joint and the support bearing/cross member to the vehicle floor is supported without any damage to the bearing.
The pairing of materials on the inner and outer ring is selected such that the outer ring consists of plastic slides on a chromium layer of the metallic inner ring. The connection of the drive shaft guided through in the central support tube or of a central shaft tube with the engine-side output shaft takes place, for example, by way of a spirally toothed end of the shaft which engages in a corresponding toothing in a sleeve of the output shaft.
Other solutions of the connection between the output shaft and the central shaft may consist of a constant-velocity joint or an elastomer disk.
Advantageously, the torque-transmitting joint, particularly a cardan joint, is provided with a centric opening. As a result, it becomes possible to shift the clutch shaft from a drive position into a repair position axially in the central shaft tube so that a fast removal of the clutch can take place.
In order to achieve an effective uncoupling of vibrations between the engine and the transmission with a rigidly connected central support tube, the central support tube must be light and resistant to bending, in which case a reduced torsional rigidity and a high resistance to bending is desirable. A central support tube made of a fiber composite material is suitable for this purpose.
Because of the low excitation of vibrations, the articulated connection to the central support tube or to the drive shaft must be arranged as closely as possible to the engine. Furthermore, the bearing sites of the drive shaft must be fixed in the area of a low excitation of the central support tube.